Galileo Galilei once said in the 17th century that “anyone who understands geometry can understand everything in this world.” But he had never heard of molecules, atoms or even smaller components. These days we would imitate Galileo by saying “anyone who understands the processes inside atoms and molecules understands the world.” This nano world has its own unique appeal: something that is invisible to the naked eye, yet has dimensions that the mind still requires images/comparisons to understand, is a source of tremendous fascination. Even if we are a long way from understanding these processes, we now know one thing for certain: these days, decisive technological progress is made in the world of the minuscule. Specific examples of this come from the areas of gene technology, materials research and electronics on a daily basis.
As a result, nanotechnologies have become the focal point of research and development – not only in industry but also in politics. For example, in March 2004, the German Federal Government launched the German innovation initiative for nanotechnology under the slogan “Nanotechnology Conquers Markets”. According to a press release by the German Federal Ministry of Education and Research (BMBF), € 200 million in funding will be made available to four leading-edge innovations over the next four years.
However, there is still some debate about how to define the term “nanotechnology”. While some see the essence of nanotechnology as the creation of a large entity from the minutest components by means of partly self-organizing processes, such as car paint consisting of nanoparticles, others simply regard the scale of particles or structures as the area of crucial significance. Scientists set a value of 100 nanometers as the “limit”. A BMBF brochure argues: “It [nanotechnology] does not, therefore, represent a basic technology in the classical sense – one with clearly defined parameters. Instead, it describes a new interdisciplinary approach that will help us to make further progress in the fields of biotechnology, electronics, optics and new materials.”
There seems to be no end to the debate, with definitions continuing to clash and overlap. One thing is for sure, though, and that is the importance of nanotechnologies as a driving force for technological progress.
Nanostructuring – the largest area of application for nanotechnologies
Financially, the most important area of application for nanotechnologies is microelectronics or nanoelectronics. The significance of the influence that nanotechnologies have here can be seen in two developments from everyday life. The triumphant progress of the computer in all its variants – from the PDA to the notebook, laptop and classical tower computer – would not have been possible without the continuous development of integrated circuits, or more specifically the progressive miniaturization of these circuits. Another example is something we all carry around with us every day: the mobile phone. This is perhaps the clearest example of what miniaturization means and what it can achieve. Who, 15 years ago, would have dared predict that there would be cable-free portable telephones for everyone, offering virtually the same range of services as a computer?
The quasi-formula for the achievement of this progress is the much-cited Moore’s Law. Gordon Moore, co-founder of Intel, predicted that the number of transistors in a given area would double every 18 months. This prediction has become the benchmark for action in the entire chip industry and its supplier industry. Roadmaps to ensure that these industries live up to this prediction have been developed for all chip fabrication processes and are discussed and updated regularly.
Lithography optics as a driver for Moore’s Law
Optical lithography, which is assigned a key role in structuring, plays a decisive role in making Gordon Moore’s prediction come true. The process of projecting semiconductor structures from the mask onto the wafer is the ultimate accelerator for miniaturization. Carl Zeiss has led the way in developing and manufacturing highly precise optics for optical lithography since the 1960s. The first step involved deriving optics from photographic lenses to reduce the circuits drawn by hand on the drawing-board. Current lithography optics, however, weigh up to a ton, have a diameter of more than half a meter and consist of several dozen single lenses. Future relevance was often disputed in the course of the development of optical lithography, but it ultimately overcame all rival technologies due to cost efficiency and investment reliability.
The progress of optical lithography is mainly characterized by ever shorter wavelengths for imaging. The current workhorses in the chip factories of the world operate at 365nm, 248nm and 193nm. With this wavelength it is possible to produce structures of well under 100 nanometers in width, thereby penetrating the world of nanotechnology. And the next leap in resolution with this wavelength is already in sight. Through the introduction of an immersion liquid between the last objective lens and the wafer, the so-called “numerical aperture”, the objective aperture, can be increased beyond a value of 1.0, thereby also increasing the resolution, as this was done in immersion microscopes as far back as the 19th century. Today’s “dry systems” already achieve a resolution of 65 nm, with 55 nm even being demonstrated in the laboratory. Immersion technology takes a further 10 nm off this, at the very least, making structure widths of 45 nm possible. Feasibility in principle was already demonstrated more than a year ago. With a constantly high numerical aperture (NA), in scanning mode the same resolution was shown as in the dry system, yet with significantly greater depth of field. This widens many process windows in chip fabrication and ultimately helps increase the yield. Future developments are expected to take the NA beyond a value of 1.0, thereby improving resolution still further.
But that’s not all. The next generation in optical lithography, known as EUV lithography, is already in the starting blocks and ready to break through the predicted limits once again. Based on a soft x-ray with a 13 nm wavelength, Carl Zeiss SMT has development mirror optics that enable a resolution of considerably less than 40 nanometers. Initial test systems have already been installed at International Sematech, as well as at one of the world’s leading chip manufacturers. In tests, it has already been possible to produce 30-nanometer structures. This is a technology that offers the potential of miniaturizing nanoelectrical components continuously for many years.
Yet even the manufacture of the lenses and mirrors for lithography is applied nanotechnology according to the above definition. The surfaces of the optics have to be made with a precision that could well be unique in industrial production. The standards set by mathematicians must be observed to within a few atomic positions. What this means can best be explained with a comparison: if one were to expand the surface of an EUV mirror to an area the size of Germany, the deviation from the pre-defined form would have to be no greater than a few millimeters. Developing technologies and strategies for the standard, reproducible manufacture and measurement of such precise areas is the greatest challenge Carl Zeiss SMT AG has faced to date.
Mask measuring technology and repair
Photomasks play a major role in the realization of ever newer and better functionalities in nanoelectronics. These are the original templates for chip fabrication. The high degree of complexity of these photomasks means that highly precise systems are needed to measure, verify and repair them. This task is expertly performed by AIMS™ (Aerial Image Measurement System) technology from Carl Zeiss SMT AG. Since its launch 10 years ago, AIMS technology has established itself as an industry standard in all major mask houses. It works by reproducing the optical image of the mask in the wafer scanner. The mask structure that is to be analyzed is magnified and displayed on a high-precision camera under conditions that are equivalent to photolithographic exposure. Using the subsequent quantitative analysis of the images acquired electronically with the help of specialist software, the user can check whether the mask structure contains any imperfections that are of relevance lithographically. There are two different types of imperfection: those that do not affect wafer production and therefore do not have to be repaired, and those elements of damage that require correction using a mask repair system, such as the Carl Zeiss SMT system MeRiT™, or, in extreme cases, the manufacture of a new mask. AIMS™ enables semiconductor manufacturers and mask houses to evaluate and repair defects quickly and economically without any wafer exposure whatsoever. As a result, AIMS™ systems are an indispensable tool in mask houses for assuring the quality of ongoing mask production, and are also used for the development of new mask generations prior to the availability of the actual wafer steppers. The development of the AIMS™ product range follows the optical lithography roadmap and comprises systems for the exposure wavelengths 365nm, 248nm and 193nm, with numerical apertures adjusted to the scanner. For immersion lithography, the Semiconductor Metrology Systems Division of SMT has entered into a joint venture with International Sematech with a view to defining the requirements for the instruments and promoting instrument development.
Mask repair
With respect to the issue of mask repairs, as addressed above, the year 2003 saw Carl Zeiss SMT and Rossdorf, Germany-based NaWoTec GmbH awarded the German industry innovation prize for a joint development. The MeRiT™ mask repair system, as it is called, is based on an electron beam system that induces chemical reactions and makes it possible to repair defects in the nanometer range by deposing or etching materials. A gas injection system is used to bring reaction gases into the domain of an electron beam. Excited by the electrons, the gas molecules adsorbed on the surface of the mask become chemically excited, either leaving behind precipitations (or “deposits” as they are known) or etching grooves into the material. Structures down to 10-22 nanometers can therefore be produced or removed with a positioning accuracy of 10 nanometers (3 sigma). Consequently, the system addresses the 65 nanometer node for the 193 nm exposure wavelength, with the 45 nanometer node next on the list of targets. As a result, imperfections classed as critical, i.e. “printable”, by the AIMS™ system can be repaired effectively and with impressive reliability. In a closed loop, the success of the repair is then evaluated again in the AIMS™ system.
The MeRiT™ mask repair system is also able to effectively repair the absorber coating (tantalum nitrite) of masks for the new procedure of EUV lithography, which means that the important question of mask repair for EUV lithography can already be given a positive answer. In other projects we are currently examining whether the system can even “cure” defects (tiny dust particles, for example) within the reflective molybdenum/silica coats on EUV masks. The prospects are very promising.
Materials analysis
Another important element in the quest to decipher the nano world is materials research. Electron and ion beam systems play a crucial role in this right from the outset. After all, it is at the boundary layers between different materials that the physical and technical effects occur that are responsible for the function of complex structures, such as semiconductor components. However, also of immense interest for the predictability of important properties, such as tensile strength and temperature stability, is the precise, atomic structure of metal alloys. Tests and the manufacture of cross-sections in materials and components can be realized in real time with Carl Zeiss SMT systems, such as the CrossBeam® line, a combined electron/ion beam system. The ion beam column cuts into a specimen in real time while it is observed under an extremely high-resolution electron microscope. This means that there is no need for complex preparations in order to analyze materials or components and determine causes of imperfections. The SMT electron beam systems are also put to versatile use in semiconductor technology. Materials research and development, component development and process development are inconceivable without the visualization and analysis possibilities offered by high-quality scanning and transmission electron beam systems like those developed and supplied globally by Carl Zeiss SMT as part of a wide product portfolio.
Carl Zeiss SMT AG
Under the motto “Enabling the Nano-Age World”®, Carl Zeiss SMT AG sees itself as a problem-solver for many high technology applications in semiconductor technology and materials research/analysis. Building on core competences in optics, measuring technology and electron as well as ion beam technology, it offers a portfolio that perfectly supports the entire process from semiconductor manufacture right through to the analysis of imperfections.
The Carl Zeiss SMT group, with around 1,800 employees, achieved turnover of € 560 million in the 2003/2004 financial year, an increase of 25% over the previous year. Carl Zeiss SMT, with its partner ASML, is the global market leader for wafer steppers and scanners. Around 400 employees are involved in research and development, with approximately 14% of total revenue invested in the work they perform. |